Tap for rolling internal threads



April 13, 1965 P. A. KOEHLER TAP FOR ROLLING INTERNAL THREADS Original Filed Nov. 9, 1959 Fig. 2

1 N VE NTOR ATTORNEY United States Patent 'ice 3,177,691 TAP FOR ROLLING INTERNAL THREADS Paul A. Koehler, deceased, late of Chagrin Falls, Ohio, by Marian E. Koehler, executrix, Chagrin Falls, Ohio (1535 Sherhrook Road, South Euclid, Ohio) Original application Nov. 9, 1959, Ser. No. 851,804, new Patent No. 3,069,940, dated Dec. 25, 1962. Divided and this application July 3, 1962, Ser. No. 207,436

1 Claim. (Cl. 7267) This application is a division of co-pending application Serial No. 851,804 filed November 9, 1959, now Patent No. 3,069,940 granted December 25, 1962.

This invention relates to taps for rolling internal threads.

Although there have been prior attempts to provide taps for rolling internal threads, such taps are not in widespread use despite the fact that rolled threads are stronger and smoother than cut threads.

One of the principal reasons why such prior taps have not achieved general commercial acceptance is that the designs have been such as to be unable to provide sufiicient rigidity for the thread forming rolls to withstand the side loads imposed thereon without deflecting, resulting in inaccurate and non-uniform sizing of the thread.

Accordingly, it is an object of the present invention to provide a tap for rolling internal threads in which the holder for the thread forming rolls is so constructed as to rigidly support the thread forming rolls against deflection under side loads thereon.

It is another object to provide a tap of the type described in which a one piece holder supports the thread forming rolls at both ends thereof for maximum rigidity against deflection of such rolls.

It is another object to provide an internal thread rolling tap with a plurality of thread forming rolls and with a simple means for adjusting the relative radial position of one thread forming roll with respect to another for accurately controlling the size of the thread to be formed in a work piece.

It is another object to provide a tap for rolling internal threads in which the holder for the thread forming rolls is one piece for maximum rigidity and has recesses for containing the thread forming rolls which are easy to machine.

Other objects will become apparent from the drawings and from the following description in which:

FIG. 1 is a side view of the tap,

FIG. 2 is an end view,

FIG. 3 is acne-quarter section view along the lines 33 of FIG. 2, and

FIG. 4 is a section along the lines 4-4 of FIG. 3.

Holder 40 has a shank 41 at one end and at the other end has rolls supporting portions 42 and 43 which are spaced from each other but which are integrally connected with the holder 40 by means of an axially extending portion 44. The latter has a pair of recesses 45 formed therein for receiving thread forming rolls 46. Only two rolls 46 are illustrated but it is understood that the number of rolls employed is optional.

Roll supporting portions 42 and 43 have bores 49 and 50 formed on opposite sidesof each recess 45 and axially aligned therewith. Bores 49 and 50 form bearing surfaces for pins 53 therein upon which the rolls 46 are mounted. In addition, the bores 50 extend to the opposite end of the holder.

3,177,691 Patented Apr. 13, 1965 Each set of bores 49-50 and recesses 45 have a common longitudinal axis 57 which is parallel to the longitudinal axis 58 of the holder in one plane, as viewed in FIG. 3, and which is at an angle 59 to the axis 58 when viewed in another plane which is at right angles to the first mentioned plane, as shown in FIG. 1.

The end surfaces of the recesses 45 are normal to the respective axis 57. Bore 49 is of larger diameter but concentric with bore 50. Mounted in each set of bores 49 and 50 are pins 53. Each pin 53 has concentric cylindrical end portions 62 and 63 and an intermediate cylindrical portion 64 whose axis is parallel to but offset from the axis of the end portions so that the cylindrical portion 64 is eccentric to the cylindrical portion 62 and 63.

The thread forming rolls 46 are mounted on the intermediate portions of the pins and have a. close rotating fit thereon. Since the intermediate portions 64 of the pins are eccentric with the end portion 62 and 63, rotation of the pin Within the pin supporting bores 49 and 50 will cause the roll 46 which is mounted on the pin being rotated to assume various adjusted lateral positions with respect to the other roll 46. By this means, the pitch diameter of the thread being rolled into the work piece may be adjustably varied. When the pins 53 have been rotated to their proper setting, they are clamped in such rotated position by set screws threaded into the holder 40. The set screws also prevent endwise displacement of the pins 53.

When rolling the thread, holder 40 is rotated relative to the work piece, the latter being shown in dotted outline in FIG. 3. As the tap enters the work piece and rolls the thread therein, extremely high pressure is exerted in a radially inward direction upon the rolls. In order that the threads in the work piece be accurately formed with a uniform pitch diameter, it is necessary that the rolls 46 be rigidly supported against radially inward deflection due to such inward pressure. Maximum support for such rolls is obtained by making the rolls supporting portions 42 and 43 integral with each other and with holder 40, and by having such portions of imperforate transverse cross section as far as possible. Axially extending portion 44 between the roll supporting portions 42 and 43 is provided with a maximum of cross section by making rolls 46 of a relatively small diameter with recesses 45 fitting closely thereabout so that a substantial thickness of metal is pro vided at the central portion of the axially extending portion 44 as well as between recesses 45.

In the invention as described the holder provides a very rigid support against radially inward deflection of the rolls due to pressure of the same against the work piece. Such very rigid support is brought about by the fact that the roll supporting portions 42 and 43 are integral with the holder and are connected by the axially extending portion 44 which is of maximum and imperforate cross section and which is integral with portions 42 and 43.

What is claimed is:

A tap for rolling internal threads in a Work piece, said tap including an integral one-piece holder and at least one thread forming roll having an annular thread forming rib thereon, a shaft having a central portion on which said roll is rotatably mounted, said shaft having axially aligned front and rear end portions eccentric to said central portion and journalled respectively in front. and rear circular bearing portions defining integral portions of said holder with the axis of said central shaft portion being generally longitudinal of said holder and transversely spaced from q r-Z the longitudinal axis of said holder, said shaft being rotatable in said bearing portions whereby said transverse spacing may be varied due to said eccentricity, said front shaft portion and front bearing portion extending beyond said rear and central shaft portions in all radial directions whereby said shaft may be inserted into said holder through the front bearing portion thereof, said front shaft portion having at its free end on adjusting means whereby said shaft may be rotated for varying said transverse spacmeans and said locking means may enter work piece during the process of rolling threads therein with said tap.

References Cited by the Examiner UNITED STATES PATENTS 885,068 4/08 Moy et al. 80-6 2,349,863 5/44 Hallberg 806 3,089,362 5/63 Hill 80-58 FOREIGN PATENTS 1,086,661 8/60 Germany.

CHARLES W. LANHAM, Primary Examiner.

MICHAEL V. BRINDISI, Examiner. 

